1. Field of the Invention
The invention relates to a circuit arrangement suitable for high-frequency operation of a discharge lamp, provided with
input terminals for connection to a low-frequency supply voltage source, PA1 rectifying means coupled to the input terminals for rectifying a low-frequency supply voltage supplied by the low-frequency supply voltage source, PA1 a first branch comprising first capacitive means and connected to the rectifying means, PA1 a DC-AC converter coupled to the first capacitive means for generating a high-frequency current from a direct voltage present across the first capacitive means, and PA1 a further branch of which a first end is connected to a point of the DC-AC converter at which a high-frequency voltage is present during lamp operation and of which a further end is coupled to the rectifying means.
2. Description of the Prior Art
High-frequency operation of a discharge lamp in this connection is understood to mean operation at an operating frequency of approximately 10 kHz and higher. A low-frequency supply voltage source is understood to mean, for example, a substantially sinusoidal mains voltage with a frequency of, for example, 50 or 60 Hz.
Such a circuit arrangement is known from U.S. Pat. No. 4,782,268. The known circuit arrangement comprises a DC-AC converter consisting of a bridge circuit. The further branch comprises both inductive and capacitive means and in addition two diodes. A first end of the further branch is connected to a junction point of two switching elements forming part of the bridge circuit. A further end of the further branch is connected to an output of the rectifying means. It is achieved by means of the further branch that the circuit arrangement behaves like an ohmic resistance to a considerable degree during lamp operation. As a result, the circuit arrangement causes only a comparatively small amount of interference in the low-frequency supply voltage source and a high power factor is realised by the circuit arrangement during lamp operation.
A disadvantage of the known circuit arrangement is that, in addition to the diodes forming part of the rectifying means, further diodes are necessary, i.e. the two diodes in the further branch, for realising the favourable properties of the circuit arrangement as regards mains interference and power factor.